Cotton (Gossypium hirsutum L.), as the greatest source of natural fibre, is one of the most valuable crops grown worldwide. Like most major field crops, irrigation and nitrogen (N) fertilization are the most important two factors for improving cotton yield in term of quantity and quality. As these represent the largest inputs in the best management practice for cotton production, the optimum water and N-fertilizer requirements of cotton should be closely evaluated.
The Rassafa cotton cultivar is a relatively new variety grown in the dry areas of the Eastern Mediterranean region. Farmers have targeted the higher seed cotton yield and they assume the greater yields would need augmented N fertilizer and water quantity. So, water and nitrogen fertilizer requirements of this new cultivar need to be quantified and optimized. In this context, as drip irrigation system is flexible enough to water both sides of plant row either simultaneously or alternatively, this study implemented full irrigation (FI) and both the regulated fixed partial rootzone drying irrigation (FPRD) (also called as regulated deficit irrigation) and alternate partial rootzone drying irrigation (APRD) through the drip fertigation system.
A field experiment was carried out for two consecutive years (2014 and 2015) to report the effects of different N-levels and drip irrigation modes on seed cotton yield (SCY), dry matter (DM), reproductive to vegetative ratio (RVR), and water productivity (WP). Results may contribute to introduce practical alternatives in the context of sustainable crop production, environment protection, and minimizing production costs. Treatments consisted of five different N-rates (0, 50, 100, 150, and 200 kg N ha-1), and three irrigation modes: full irrigation (FI), FPRD80, and APRD80. They received 100, 80, and 80% of the seasonal water use, respectively. Cotton was irrigated when soil moisture in the specified active root depth was 80% of the field capacity as designated by the neutron probe.
Results indicated that the tested cotton crop cultivar was found to be responsive to the nitrogen fertilizer and drip irrigation modes. Seed cotton and dry matter yields, and water productivity could be maximized at an optimal nitrogen applied amount of about 140 kg N ha-1. Results suggested that yield, reproductive to vegetative ratio, and water productivity were influenced by environmental conditions between years under the alternate partial root-zone drying irrigation (APRD). Both full and fixed partial rootzone drying irrigation modes (FI and FPRD) performed consistently over years, but yields and water productivity were found to be higher under full irrigation.
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